<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>compute / watch </title>
    <script src="https://unpkg.com/vue/dist/vue.js"></script>

    <script src="https://unpkg.com/axios@0.12.0/dist/axios.min.js"></script>
    <script src="https://unpkg.com/lodash@4.13.1/lodash.min.js"></script>
</head>
<body>
<div id="watchCompute"> {{ fullName }}</div>
<div id="demo"> {{ computeFullName }}</div>
<div id="watch-input">
    <p>
        Ask a yes/no question:
        <input v-model="question">
    </p>
    <p>{{ answer }}</p>
</div>

<script>

    var vm = new Vue({
        el: '#watchCompute',
        data: {
            firstName: 'Foo',
            lastName: 'Bar',
            fullName: 'Foo Bar'
        },
        watch: {
            firstName: function (val) {
                this.fullName = val + ' ' + this.lastName
            },
            lastName: function (val) {
                this.fullName = this.firstName + ' ' + val
            }
        }
    })

    //    上面代码是命令式的和重复的。跟计算属性对比：这样更好，不是吗？


    var vm = new Vue({
        el: '#demo',
        data: {
            firstName: 'daniel',
            lastName: 'kong'
        },
        computed: {
            computeFullName: {
                // getter
                get: function () {
                    return this.firstName + ' ' + this.lastName
                },
                /*setter
                 现在在运行 vm.fullName = 'John Doe' 时，
                 setter 会被调用， vm.firstName 和 vm.lastName 也会被对应更新。*/

                set: function (newValue) {
                    var names = newValue.split(' ')
                    this.firstName = names[0]
                    this.lastName = names[names.length - 1]
                }
            }
        }
    })

    var watchInputVM = new Vue({
        el: '#watch-input',
        data: {
            question: '',
            answer: 'I cannot give you an answer until you ask a question!'
        },
        watch: {
            // 如果 question 发生改变，这个函数就会运行
            question: function (newQuestion) {
                this.answer = 'Waiting for you to stop typing...'
                this.getAnswer()
            }
        },
        methods: {
            // _.debounce 是一个通过 lodash 限制操作频率的函数。
            // 在这个例子中，我们希望限制访问yesno.wtf/api的频率
            // ajax请求直到用户输入完毕才会发出
            // 学习更多关于 _.debounce function (and its cousin
            // _.throttle), 参考: https://lodash.com/docs#debounce
            getAnswer: _.debounce(
                    function () {
                        var vm = this
                        if (this.question.indexOf('?') === -1) {
                            vm.answer = 'Questions usually contain a question mark. ;-)'
                            return
                        }
                        vm.answer = 'Thinking...'
                        axios.get('https://yesno.wtf/api')
                                .then(function (response) {
                                    vm.answer = _.capitalize(response.data.answer)
                                })
                                .catch(function (error) {
                                    vm.answer = 'Error! Could not reach the API. ' + error
                                })
                    },
                    // 这是我们为用户停止输入等待的毫秒数
                    1000
            )
        }
    })

</script>
</body>
</html>
